The Animal Surgery core is designed to perform all the operative procedures required for the testing of each of the overall Group Hypotheses and for the Specific Aims of each of the four Projects. It is staffed by the Project director and the animal surgery technician. Objectives and functions of the core are as follows: 1) to perform all of the animal operative procedures needed for the entire Project; 2) to monitor the health status of the operated animals; 3) to schedule experiments and operations; 4) to assist in tissue removal and distribution to the Project laboratories; and 5) to prepare muscles that are used for the in vitro testing of contractile properties. Operations to be performed are standard, nerve-implant, and nerve-intact muscle grafts, nerve transections and permanent denervations, as well as injections of local anesthetics for the purpose of producing muscle fiber degeneration. The maintenance of the experimental animals, along with dealing with animal pathology, will be supervised by the unit for laboratory Animal Medicine at the University of Michigan.